Chronic Radium-226 Bioaccumulation and Toxicity in the Aquatic Invertebrate Daphnia magna

Area of Science:

• Environmental Toxicology
• Ecotoxicology
• Radiochemistry

Background:

• Mining operations, particularly uranium mining, produce by-products containing radium-226 (²²⁶Ra).
• ²²⁶Ra is a long-lived, bioaccumulative radionuclide and a calcium analog.
• Existing Canadian discharge regulations for ²²⁶Ra may not adequately protect aquatic organisms, and a federal water quality guideline is absent.

Purpose of the Study:

• To assess the chronic toxicity and bioaccumulation of radium-226 (²²⁶Ra) in the model aquatic invertebrate Daphnia magna.
• To provide data for establishing protective water quality guidelines for ²²⁶Ra in Canadian aquatic ecosystems.

Main Methods:

• Conducted two 21-day chronic toxicity tests on Daphnia magna, measuring survival and reproduction.
• Performed experiments on reduced water hardness, multigenerational effects, and bioaccumulation.
• Measured radium-226 (²²⁶Ra) activity concentrations and bioaccumulation factors (BAF).

Main Results:

• A high activity concentration of ²²⁶Ra (nominal 50 Bq/L) significantly impacted Daphnia magna survival.
• ²²⁶Ra bioaccumulated in Daphnia magna with a bioaccumulation factor (BAF) of 72.8.
• Current Canadian Metal and Diamond Mining Effluent Regulations (MDMER) limits (0.37–1.11 Bq/L) are unlikely to prevent toxic effects in aquatic invertebrates.

Conclusions:

• Radium-226 (²²⁶Ra) poses a significant toxicological risk to aquatic invertebrates like Daphnia magna at concentrations relevant to mining effluents.
• The bioaccumulation of ²²⁶Ra in aquatic organisms is a concern.
• Current Canadian effluent regulations for ²²⁶Ra may be insufficient to protect sensitive aquatic species downstream of mining operations.